In order to properly assist you, we'll need a bit more information:
Browser and version
In which versions of which browsers are you experiencing this issue? Would it be in all browsers, or just on some browsers? For instance if it happens in IE, does it happen in all IE browsers, or just few of them? Also, does it happen normally, or [in the case of IE] you have to switch browser version from the toolbar
What type of zooming are we talking about? There is the so called Text zooming, which zooms just the text and parts of the page (depending on the actual styles) and then you have full page zoom which zooms the entire page, not just the text.
You say "sometimes". But does it mean sometimes on the same page, or sometimes on different pages? Having different outcome performing the same actions on the same page will be really unlikely, but on different pages it's more or less expected.
It will be nice if we could have a simple testcase that has the issue. Be it a live URL or a sample of your project -- it will help us find the issue [ why pages zoom differently ].
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed